Read Mark 3:31-35 Note: speaking of God’s will as it is mentioned in the Third Petition of the Lord’s Prayer, Luther’s Small Catechism uses Deuteronomy 4:2, John 6:40, 1 Timothy 2:4, and 1 Thessalonians 4:3 to say, “It is God’s will that His name be kept holy and that His kingdom come, that is, that His Word be taught correctly and that sinners be brought to faith in Christ and lead godly lives" (LSC (1986), pp.181-82).
Note: in The People’s Bible Commentary:Mark, page 59, Harold E. Wicke gives his readers a similar answer by saying, "Doing the will of God is believing and trusting in what he has done for us through Christ Jesus. That will also bring with it a love for all the other commands of our God."